Process for expanding metal sandwiches



United States Patent 3,247,590 PROCESS FOR EXPANDING METAL SANDWICHES Albert Perlick, Werdohl-Kleinhamrner, and Anna-Ilse Siegmuud and Alfred Gareis, Werdohl-Eveking, Germany, assignors to Vereinigte Deutsche Metallwerke Alrtiengesellschaft Zeilweg, Frankfurt am Main, Heddernheim, Germany No Drawing. Filed June 4, 1963, Ser. No. 285,237

4 Claims. (Cl. 29455) The invention relates to a process for expanding metal sandwiches composed of a plate printed at various points with a parting agent, and of an additional plate which can be of the same size, the two plates being welded together by rolling. The plates remain unwelded in the printed areas, and there they can be ballooned outward by gases or liquids under pressure. These known procedures can be performed with all metals, particularly those that can be pressure welded. Aluminum is especially well suited, since pressure welding can be used and protective gas is unnecessary during the welding process.

Graphite of colloidal fineness has proven best as a parting agent. This substance has with respect to other known parting agents, such as chalk, quartz or lime, the great advantage of also having lubricating properties at the hotrolling temperatures involved (500 C. in the case of aluminum), and of providing adequate parting even when printed on in a very thin layer.

As is known, in the prior art printing processes, such as screen printing for example, the film thicknesses realized fluctuate above and below an average, and in order to achieve reliability, the graphite must be applied in excess. The excess graphite, however, adheres after ballooning to the interior walls of the cavities as an undesired impurity which should be removed.

It is known to use a liquid such as water or methyl alcohol for ballooning the cavities. Following the expanding, the liquid is removed from the cavities, and the cavities are then rinsed with wet steam and finally dried with hot compressed air. This procedure is complicated and expensive. Also, the interior Walls of the cavities corrode, since some graphite remains and the graphite particles and themetal milieu in which they are embedded form with water innumerable local electrical cells. It is also known to expand with compressed gas. This procedure, however, has the disadvantage that too much residual graphite remains in the cavities, and it is necessary to remove this by washing it out with a liquid, for example.

It has now been found surprisingly that, when ballooning with a compressed gas, considerably less graphite remains adhering to the cavity walls if a low-boiling, very dry gas is used. According to the invention, a very dry, compressed gas is used for the expanding. Thus, there is used a gas having a boiling point below 150 C., and which contains a maximum of 30 mg. of water per Nmfi. Nmfi means cubic meters under normal conditions (0 C., 760 Torr). Air, containing a maximum of 30 mg. water per NIIL3, has proven to be advantageous. On the other hand, carbon dioxide or ethane fail when used for the ballooning, because the graphite coating is not released from the cavity walls even when these gases contain less than 30 mg. Water per Nm. These two gases boil at 79 and --89 C., respectively. It can be assumed that they are adsorbed so strongly by the graphite that an effect occurs which is comparable to that of water vapor. On the other hand, the graphite coating is released extensively when use is made of nitrogen, oxygen, argon or hydrogen, providing these gases contain less than 30 mg.

water per Nmfi.

3,247,590 Patented Apr. 26, 1966 Thus, the invention provides an improvement in the production of open metal work wherein a sandwich of metal plates bonded together at loci which are to be bonded together in the open metal work product and separated by graphite in the areas to be expanded to provide the open sandwich, and wherein the expanding is eifected by the utilization of fluid pressure. According to the invention, a gas is employed as the fluid and the gas has a boiling point of less than about -l50 C. and contains at most 30 mg. of water per Nm.

The following examples serve to explain the idea of the invention. In these examples the surface of an aluminum plate is roughened and spot printed with graphite. An unprinted plate of the same size is placed over it, and this sandwich is then rolled hot at 500 C. becoming quadrupled.

EXAMPLE 1 A graphite coating of 6500 mg./m. was printed on. After rolling, one eighth thereof, namely about 800 mg./ 111. remained on the internal surfaces of the not yet ballooned cavities. When they were ballooned with compressed air at atmospheres, containing 0.2 mg. of water per Nm. only 360 mg./m. of graphite still remained on the interior surfaces. If, however, the ballooning was done with air at the same pressure, but with a water content of 180 mg./Nm. 770 rug/m. of graphite remained on the interior surfaces after ballooning.

EXAMPLE 2 If only 2000 mg./m. of graphite were printed on, there were 250 mg./rn. of graphite on the interior surfaces of the cavities before ballooning. Under the same ballooning conditions as in Example 1, graphite residues of and 230 mg./m. were found.

EXAMPLE 3 If the ballooning was done with carbon dioxide at 55 atmospheres containing 15 mg/Nm. of water, 560 mg./ m. and 230 mg./m. of graphite residues were found when the interior surfaces of the unballooned cavities had previously been covered with 650 and 250 mg./m. respectively.

\Vhile the invention has been described with respect to particular embodiments thereof, these embodiments are merely representative of the invention, and do not define the limits thereof.

What is claimed is:

1. In the production of open metal Work wherein a sandwich of metal plates bonded together at loci which are to be bonded together in the open metal work product, and separated by graphite in the areas to be expanded to provide the open structure, is expanded by fluid pressure applied between the plates, the improvement which comprises employing as said fluid a gas having a boiling point of less than about 150 C. and which contains at most 30 mg. of water per Nmfi.

2. Process according to claim 1, wherein the metal plates are aluminum and the bonding is by welds.

3. Process according to claim 1, wherein the gas is air.

4. Process according to claim 2, wherein the gas is air.

References Cited by the Examiner UNITED STATES PATENTS 2,212,481 8/ 1940 Sendzimir. 2,941,280 6/1960 Heuer et al 29157.3 3,018,543 1/1962 Beck 29157.3

JOHN F. CAMPBELL, Primary Examiner. 

1. IN THE PRODUCTION OF OPEN METAL WORK WHEREIN A SANDWICH OF METAL PLATES BONDED TOGETHER AT LOCI WHICH ARE TO BE BONDED TOGETHER IN THE OPEN METAL WORK PRODUCT, AND SEPARATED BY GRAPHITE IN THE AREAS TO BE EXPANDED TO PROVIDE THE OPEN STRUCTURE, IS EXPANDED BY FLUID PRESSURE APPLIED BETWEEN THE PLATES, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS SAID FLUID A GAS HAVING A BOILING POINT OF LESS THAN ABOUT -150*C. AND WHICH CONTAINS AT MOST 30 MG. OF WATER PER NM.3. 